Heat pumps cut energy costs and reduce carbon emissions by generating heat from free, renewable energy from our environment – the air, ground or water. This leads many householders wondering how heat pumps manage to do their job when we need them most as temperatures plummet.
This post examines how different types of heat pumps continue to work in winter to keep homes warm and provide domestic hot water.
How Does A Heat Pump Operate?
The laws of thermodynamics tell us that heat energy always moves from a warmer spot to a cooler area. But heat pumps take thermal energy in the opposite direction – from the cooler outdoors to inside your home.
A heat pump cycle consists of three main elements:
- Collecting natural heat.
- Increasing the temperature.
- Releasing the heat to warm the home/provide hot water.
A heat pump’s main source of energy is the naturally occurring ambient heat which can be extracted from the ground, air, or water (such as rivers and lakes).
Electricity is required to run the heat pump and enable it to extract thermal energy which is delivered into the heat exchanger. Here, refrigerant is present and this absorbs the heat and evaporates into a gas.
This gas is then compressed which will boost its temperature. Any heat generated can be released into the central heating system (via radiators or underfloor heating). Most types of heat pumps are also capable of providing domestic hot water.
Heat Pumps in Winter
Now you understand how heat pumps work, the question remains of how they can take heat from outside when the weather turns chilly.
Heat pumps operate in the same way in winter as they do any other time of year, but some have to work harder. This is because more energy needs to be extracted from a cooler environmental source to meet heating and hot water requirements.
Climate change has made winter in the UK around 1°C warmer over the past century. Temperatures during December, January and February now average 2°C to 7°C.
But the mercury still often dips below freezing point – 0°C, when water turns to ice. However, heat pumps can still provide home heating in winter, and they do it more effectively than other types of heating systems.
Why Ambient Heat Is Always Available
As temperatures fall, thermal energy remains available in the air, ground and water. If there was no ambient heat whatsoever, the planet would have plunged to absolute zero (-273°C ), killing everything on it in a heartbeat – don’t worry, this can never happen!
Heat pumps continue to harness ambient heat even in the coldest winter, and there’s little to no chance they will freeze up. Refrigerant in the pump’s heat exchanger will still work in temperatures of -20°C or lower.
Nevertheless, some heat pumps do need to use more electricity in winter, and this lowers energy efficiency slightly. However, they’re still far more energy efficient than a boiler, even in subzero temperatures.
What Is Heat Pump Energy Efficiency?
Heat pump energy efficiency is measured by the amount of energy the heat pump uses compared with the amount of heat it produces.
This is called the coefficient of performance (CoP). The higher that number is, the more efficient your heat pump, and the lower your electricity bills will be.
- If an appliance uses one kilowatt (kW) of electricity to generate the same amount of power, its CoP is one.
- Heat pumps typically have a CoP of at least three. This means they’re 300% energy-efficient, outputting 30kW of heat from 10kW of electricity. They achieve this high level of efficiency because they transfer heat instead of burning fuel.
- Efficiency of older gas boilers, for example, can be as low as 60%. That means 40% of the energy you pay for effectively goes to waste.
- Efficiency levels of heat pumps vary according to the source of thermal energy they use: the air, the ground, or water.
Air Source Heat Pumps Work in Winter
Air source heat pumps (ASHP) – air-to-water heat pumps – are the most common type of heat pumps in the UK. They usually last 20 years or longer, supplying radiators or underfloor heating by extracting heat from the air surrounding a property.
So how do heat pumps perform when the temperatures fall? An air source heat pump will continue to work in winter, but may cost slightly more to run as it loses some efficiency. An air source heat pump’s performance decreases because less heat is available in the air and the heat pump has to work harder and therefore requires more energy to extract it.
However, because heat pumps are 300 to 400% energy efficient in the first place, efficiency levels remain high regardless of cold weather. Most air source heat pumps will function unless temperatures drop to extreme lows which are rarely seen in the UK.
Air Source Heat Pumps in Freezing Weather Conditions
Warmth generated by rapid movement of atoms and molecules is present in the air no matter how cold it gets, even when temperatures drop below freezing. And an air source heat pump can still extract this warmth and boost it.
In some cases, air source heat pumps are capable of working in cold temperatures as low as -25°C.
Typically, when operating at -1°C, an air source heat pump’s efficiency will be around 290%. Even at -12°C, heat pump efficiency would be maintained at around 230%.
Should the heat pump start to freeze in winter, defrost mode will automatically kick in to stop the spread of ice through the system and ensure that the system continues to function.
Ground Source Heat Pumps in Winter
Ground source heat pumps (GSHP) are capable of providing heat by extracting it from the ground. Refrigerant in underground pipes extracts the thermal energy and passes it through a compressor to raise its temperature.
Ground source heat pumps work better than an air source heat pump because ground temperatures fluctuate far less than air temperatures. Even during cold weather, ground temperatures remain relatively stable throughout the year, ranging from 5°C to 15°C. This means higher levels of energy efficiency, with greater consistency.
A ground source heat pump should in most cases last more than 20 years and will provide home heating reliably across the changing seasons, averaging 450% efficiency all year round. Frost or icy conditions on a chilly day won’t lower its efficiency to any great extent.
Water Source Heat Pumps in Winter
Water source heat pumps (WSHP) are the most efficient heat pumps. They take heat from a nearby body of water such as a stream or river, lake or pond, the sea, or water under the ground.
As with a ground source heat pump, water source heat pumps work as usual in winter. This is because water temperatures, like ground temperatures, are generally more stable throughout the year, at up to 12°C, plus water is able to transfer heat 23 times more efficiently than air.
Water source heat pumps can last up to 50 years and are more efficient than both air source and ground source heat pumps, reaching up to 600% energy efficiency.
Preparing Your Heat Pump for Winter
Certain precautions will help ensure your heat pump remains as efficient as possible during cold weather. If you have an air source heat pump, for instance, keep the outdoor unit free from leaves and other garden debris that could block airflow around the machine. However, professional maintenance is crucial with all types of heat pumps.
Heat Pump Maintenance
Annual servicing and preventive maintenance by a heat pump specialist is the best way to minimise energy bills and keep your home warm no matter how cold the weather gets. This will also address any developing problems before they need expensive repairs.
Heat pump servicing and maintenance includes cleaning water filters and heat exchanger, plus visual and diagnostic system checks such as:
- Checking temperatures.
- Checking refrigerant levels.
- Making sure connections are secure.
- Testing electrical circuits.
- Checking pipework pressure and testing for leaks.
- Testing safety valves.
Pipe Insulation
Although heat pumps work in cold weather and sub-zero temperatures, pipework surrounding the system may be vulnerable to freezing. Insulating exposed pipes can prevent this and ensure the heat pump works efficiently during the colder months. It’s also recommended to lag the external pipework of your heat pump hot water cylinder.
Heat Pump Winter Efficiency Put to the Test
Studies show that heat pumps outperform fossil fuel heating systems and traditional electric heating even in the coldest weather. Researchers in the US field-tested heat pump efficiency in the northern state of Minnesota, which is known for some of the coldest winters in America. They found that air source heat pumps kept homes warm and comfortable in winter while reducing energy costs by up to 50%.
The proven efficiency of a heat pump in winter, even as temperatures nosedive, is resulting in them being installed in increasing numbers by households in a range of countries, even those with cold climates. If heat pumps can keep people snug and cosy during freezing winters, we can definitely rely on them to do the same in the temperate climate and mild winters of the UK.
Benefits of Heat Pumps
Heating our homes is a necessity that becomes more expensive as the weather gets colder. Heat pumps provide a cost-effective solution, generating far more heat than the electricity they consume. Additionally heat pump energy efficiency is likely to get better over time as the technology advances further.
Besides keeping homes warm and cosy during winter, most heat pumps can also provide hot water for kitchens and bathrooms, and some can transfer heat outside to provide a cooling system during hot weather spells.
Heat Pump Grants
A further, major benefit of heat pumps is that you may be able to get one at a substantially reduced cost or even for free. Heat pump grants of £7,500 are widely available through the Boiler Upgrade Scheme (BUS). This is open to households installing a heat pump to replace an old inefficient heating system.
Further heat pump funding – of up to 100% of the cost – comes from the Energy Company Obligation (ECO4.) This is for households on means-tested state benefits who live in the least energy-efficient homes. ECO4 flex provides similar funding to low-income households not on benefits.
Where Can I Get Good Heat Pump Advice?
If you want expert help on heat pump grants and installation, Eco Grants can help. We can check your eligibility for a heat pump grant, saving you the time and effort of trying to understand heat pump funding and eligibility.
Even if you are unable to get free heat pump funding, we can still help you find a competitive deal on heat pump installation. Get a heat pump installed and enjoy energy bill saving year round.